Macbook - HELP HELP!! I have 2 HARD DRIVES (SPLIT??!?)

I just bought a used macbook and put in the "installation CD." DUring the process, it asks which hard drive am i going to use, and show 2 hard drive icons, apparently this computer was split into two different hard drives. How can i make it one, and if not, how can i clear one. It takes 15.9 gigs (est.) to install the basics, and the 2nd hard seems like just enough, however im short, so i wanted to make space. DO i make space after i finish all the setup?!? Or while the install is done, and all running, is there an option to check which hard drive does what and if i can make my OSX run with only one hard drive. Thanks. Just for the note, im a new mac user and i apologize if this is confusing. Thanks

next after you select your language off of the top menubar you should be able to find "disk utility" in one of those menu's. select your HD and format it, that should completely erase every single file in the HD, and also eliminate that partition you have in your HD

remember that everything on your HD will be deleted, and i mean everything....